1. Technical Field
Disclosed is an antenna for being mounted on a ground plane of a board or the like to be inserted and mounted into a personal computer, for example, for performing radio communication such as information communication. Also disclosed is a communication device having the antenna.
2. Background Art
Various antennas have been proposed as antennas for performing, for example, radio communication, such as monopole antennas (for example, see Patent Document 1), patch antennas, and inverted-F antennas.
An antenna shown in FIG. 12 is an inverted-F antenna (see Patent Document 2). In this inverted-F antenna, a triangular plate-like antenna element 42 is arranged above a ground plate 41 with a space therebetween. Short-circuit plates 43 are provided on center portions of individual edges of the antenna element 42. A feeding point 44 is arranged at the barycentric position of the antenna element 42 so that power is fed from this feeding point 44 to the antenna element 42. The short-circuit plates 43 are bent down to be perpendicular to the antenna element 42. The ends of the short-circuit plates 43 are electrically connected to the ground plate 41, so that the center portions of the individual edges of the antenna element 42 are short-circuited to the ground plate 41.
An antenna shown in FIG. 13 is also an inverted-F antenna (see, Patent Document 3). In this inverted-F antenna, a radiation conductor plate 46 is arranged on a grounding conductor of a ground plate 41 or the like. The radiation conductor plate 46 is arranged so as to be substantially parallel to the grounding conductor plane. A feeding conductor plate 47 generally perpendicularly extends from an outer edge of the radiation conductor plate 46 and is connected to a feed circuit. Short-circuit conductors 48 and 49 extend generally perpendicularly from a respective plurality of positions on the outer edges of the radiation conductor plate 46. The electrical length of the radiation conductor plate 46 is set to about one-fourth of a resonant wavelength.
The short-circuit plate 48 extends from an edge, among the edges of the radiation conductor plate 46, that is adjacent to the edge provided with the feeding conductor plate 47. The short-circuit conductor plate 49 extends from an edge, among the edges of the radiation conductor plate 46, that is the same as the edge provided with the feeding conductor plate 47. The short-circuit conductor plate 48 and the short-circuit conductor plate 49 are arranged on respective parts located at different distances from the feeding conductor plate 47.    Patent Document 1: Japanese Patent No. 3457672    Patent Document 2: Japanese Patent No. 2745489    Patent Document 3: Japanese Unexamined Patent Application Publication No. 2004-312166
However, in the inverted-F antennas described above, the null point in the directivity is obtained in a plane horizontal to the ground plate 41. Thus, there has been a problem that communication may fail due to the orientation of the antenna. In addition, to increase the frequency band for the above inverted-F antenna, it is necessary to increase the height of the antenna.
In addition, in the inverted-F antennas shown in both FIG. 12 and FIG. 13, short-circuit components such as the short-circuit plates 43 and the short-circuit conductor plates 48 and 49 are formed at asymmetrical positions. Therefore, for the above inverted-F antennas shown in FIG. 12 and FIG. 13, restrictions are imposed on the antenna mounting direction. Further, to increase the antenna efficiency and frequency band for the above inverted-F antennas shown in FIG. 12 and FIG. 13, it is necessary to provide the short-circuit components near the edges of the board for utilizing resonance of the board. Therefore, there has been a problem that restrictions are imposed on the antenna mounting position.
In addition, it is difficult to provide a single patch antenna with a low-profile appearance and wide band characteristics. Therefore, the above monopole antenna disclosed in Patent Document 1 has a problem in that it is difficult to provide matching with a communication circuit when the dielectric constant of a dielectric material to be used is large.